Effect of reed canary grass cultivation on greenhouse gas emission from peat soil at controlled rewetting

Abstract

Abstract. Cultivation of bioenergy crops in rewetted peatland (paludiculture) is considered as a possible land use option to mitigate greenhouse gas (GHG) emissions. However, bioenergy crops like reed canary grass (RCG) can have a complex influence on GHG fluxes. Here we determined the effect of RCG cultivation on GHG emission from peatland rewetted to various extents. Mesocosms were manipulated to three different ground water levels (GWLs), i.e. 0, −10 and −20 cm below the soil surface in a controlled semi-field facility. Emissions of CO 2 (ecosystem respiration, ER), CH 4 and N 2 O from mesocosms with RCG and bare soil were measured at weekly to fortnightly intervals with static chamber techniques for a period of 1 year. Cultivation of RCG increased both ER and CH 4 emissions, but decreased the N 2 O emissions. The presence of RCG gave rise to 69, 75 and 85 % of total ER at −20, −10 and 0 cm GWL, respectively. However, this difference was due to decreased soil respiration at the rising GWL as the plant-derived CO 2 flux was similar at all three GWLs. For methane, 70-95 % of the total emission was due to presence of RCG, with the highest contribution at −20 cm GWL. In contrast, cultivation of RCG decreased N 2 O emission by 33-86 % with the major reductions at −10 and −20 cm GWL. In terms of global warming potential, the increase in CH 4 emissions due to RCG cultivation was more than offset by the decrease in N 2 O emissions at −10 and −20 cm GWL; at 0 cm GWL the CH 4 emissions was offset only by 23 %. CO 2 emissions from ER were obviously the dominant RCG-derived GHG flux, but aboveground biomass yields, and preliminary measurements of gross photosynthetic production, showed that ER could be more than balanced due to the photosynthetic uptake of CO 2 by RCG. Our results support that RCG cultivation could be a good land use option in terms of mitigating GHG emission from rewetted peatlands, potentially turning these ecosystems into a sink of atmospheric CO 2 .

Carbon balance of rewetted and drained peat soils used for biomass production: a mesocosm study

“…Monitoring of environmental variables was achieved by instrumentation of one of five replicate mesocosms at each GWL, assuming that the measured variables were representative for all five mesocosm replicates. Karki et al (2015) previously found that ER, CH 4 and N 2 O fluxes from instrumented and noninstrumented mesocosms (0-20 cm GWL) were similar which substantiated the assumption of similar environmental conditions among the mesocosm replicates.…”

“…Karki et al . () previously found that ER, CH 4 and N 2 O fluxes from instrumented and noninstrumented mesocosms (0–20 cm GWL) were similar which substantiated the assumption of similar environmental conditions among the mesocosm replicates.…”

Land use of drained peatlands: Greenhouse gas fluxes, plant production, and economics

“…Our simulated RCG growth, 11.7 (11.3–12.7) Mg CO 2 ha −1 year −1 , also falls within reported yields of 9–16 Mg CO 2 ha −1 year −1 for southern Sweden and Denmark, respectively (Karki et al., ; Landström, Lomakka, & Andersson, ). Interestingly, all three drained scenarios showed rather similar biomass growth rates despite different WTD settings (Figure ), which only slightly increased with lower WTD, also reported in a study by (Karki, Elsgaard, & Laerke, ). However, in their study, the WTD varied only between 0 and −20 cm.…”

“…However, the simulation showed this respiration to be sensitive to WTD and plant systems, as Scenarios 2, 3, and 4 had heterotrophic respirations (peat and litter respiration) of 14, 9, and 3 Mg CO 2 ha −1 year −1 , respectively. This is similar to heterotrophic respiration for fen rewetting and RCG cropping in Denmark at a WTD of 0 to −20 cm, and 10–20 Mg CO 2 eq ha −1 year −1 (Karki et al., ). This notwithstanding, higher respiration was found in a mesocosm study with RCG, where dark respiration measured by chambers was 40–70 Mg CO 2 ha −1 year −1 for WTD of 0–20 cm (Karki, Elsgaard, Kandel, & Laerke, ).…”

Full carbon and greenhouse gas balances of fertilized and nonfertilized reed canary grass cultivations on an abandoned peat extraction area in a dry year

“…In contrast to previous studies suggesting that RCG cultivations provide negative GHG balances and thus mitigate the GHG emissions from drained organic soils (Shurpali et al, 2010;Mander et al, 2012), both the fertilized and nonfertilized RCG systems had positive GHG balances in the current study due to the exceptionally dry conditions during the studied year. However, previous studies indicate that a negative GHG balance could be achieved by cultivating RCG in agricultural systems with elevated WTL and sufficient soil water availability (K€ atterer & Andr en, 1999;Freibauer et al, 2004;Schrier-Uijl et al, 2014;Karki et al, 2015b). Although raising the WTL in drained organic soils might result in increased CH 4 emissions, these increases have been estimated to be modest (Komulainen et al, 1998;Tuittila et al, 2000;Wilson et al, 2009;Karki et al, 2014), and are therefore unlikely to compromise the benefits gained from increased plant growth and CO 2 uptake due to sufficient water supply.…”